Abstract
The management of marine sediments after dredging has become increasingly complex. In the context of sustainable development, traditional solutions such as immersion will be increasingly regulated. More than ever, with the shortage of aggregates from quarries, dredged material could constitute a new source of materials.
In this study of the potential of using dredged marine sediments in road construction, the first objective is to determine the physical and mechanical characteristics of fine sediments dredged from a harbour in the north of France. The impacts of these materials on the environment are also explored. In the second stage, the characteristics of the fine sediment are enhanced for use as a road material. At this stage, the treatment used is compatible with industrial constraints. To decrease the water content of the fine sediments, natural decantation is employed; in addition, dredged sand is added to enhance the granular distribution and to reinforce the granular skeleton. Finally, the characteristics of the mix are enhanced by incorporating binders (cement and/or lime). The mechanical characteristics measured on the mixes are compatible with their use as a base course material. Moreover, the obtained results demonstrate the effectiveness of lime in the mixes. In terms of environmental impacts, on the basis of leaching tests and according to available thresholds developed for the use of municipal solid waste incineration (MSWI) bottom ash in road construction, the designed dredged mixes satisfy the prescribed thresholds.
1. Introduction
Dredging operations are necessary to maintain navigation in waterways and access to harbours. Each year, several 100 millions of tons of materials are dredged around the world (Boutin, 1999). These materials, ranging from rocks to clays, can contain a variable amount of organic matter and different types and levels of contaminants.
Management of dredged sediments is a worldwide problem. After dredging, traditional solutions such as dumping the sediments at sea are constrained by national and international regulations. Alternative solutions, such as terrestrial disposal, are costly and require large areas (LIFE, 2002; Grégoire, 2004). The development of beneficial use strategies for dredged sediments is therefore necessary.
5. Conclusions
For harbour managers, better management of dredged materials constitutes a key requirement to maintain navigation and to accommodate sustainable development. In this paper, an alternative solution for re-use of dredged sediments (fine dredged sediments and dredged sand) in road construction is proposed.
The methodology implemented in this study to develop the designed mixes consists of dewatering the fine sediments by decantation and improving the granular distribution by adding dredged sand. The initial decantation process is necessary to reduce dissolved salts in the pore water. The enhancement of the granular distribution improves the bearing capacity of the dredged sediments and reduces the amount of binders needed to meet the performance prescribed for the targeted use. In this study, the amount of binders added to the proposed mixes is comparable to the amount used in standard materials. These results make the designed mixes economically viable
